Marlowe and Lanier

That's true, so long as the game hasn't confirmed it yet, that possibility would always be there. (Though I'm sure it's a bad move plot-wise to use the same surprise/backstory twice, so from that angle it's unlikely Nexon would pull that again.) It's still most likely Lanier's human, though.
All the same, determining what she was would still amount to nothing, since we don't know if Lanier changed from whatever she was to a deity like Nao when she started working in Avon. For now I suppose we better leave that question mark where it is.